1. Field of the Invention
The present invention relates to technology for measuring the amount of toner on a medium.
2. Description of the Related Art
A color output by an image forming apparatus that uses toner varies depending on the environment. For example, if temperature/humidity varies, latent image potential, toner supply amount, transfer efficiency, and the like also vary. Thus, the amount of toner adhering to the photosensitive drum and the transfer belt is not constant. In view of this, technology for controlling the exposure amount, developing voltage, transfer current, and the like based on the measured amount of adhering toner has been conventionally developed. For example, according to a method described in Japanese Patent Laid-Open No. 8-327331, light is projected onto patches formed based on patch data. The amount of toner can be measured by detecting light reflected by the patches.
Japanese Patent Laid-Open No. 2008-216600 discloses an optical displacement meter. The optical displacement meter described in Japanese Patent Laid-Open No. 2008-216600 performs feedback control on the intensity of incident light such that the intensity of reflected light is appropriate. If the intensity of reflected light is too weak, accurate measurement is difficult. Further, if the intensity of reflected light is too strong, a measured value that a light reception unit outputs will be saturated. In order to cope with such problems, feedback control is used in Japanese Patent Laid-Open No. 2008-216600.
There is a difference between the amount of toner that adheres to a solid black patch and a patch formed using screen technology (including halftone technology and dithering technology). Accordingly, in order to appropriately control image formation using screen technology, it is necessary to measure the toner amount of a patch formed using screen technology. However, a patch formed using screen technology has both a portion to which toner adheres and a portion where a medium is exposed. Furthermore, a portion to which toner adheres and a portion where a medium is exposed often repeat at intervals of 100 and several tens of μm. Since the toner and the medium have different reflectance, the amount of received light will not be stable, even if feedback control is performed when measurement with respect to such a minute patch is performed.